Ophthalmic apparatus, information processing method, and storage medium

ABSTRACT

An ophthalmic apparatus includes a generation unit configured to generate 3D blood vessel data indicating a blood vessel in a fundus based on a plurality of tomographic image data indicating cross sections of the fundus, a boundary obtaining unit configured to obtain layer boundary data indicating at least one layer boundary based on 3D tomographic image data including the plurality of tomographic image data indicating the cross sections of the fundus, and a determination unit configured to determine a blood vessel intersecting with the layer boundary by comparing the 3D blood vessel data with the layer boundary data.

BACKGROUND OF THE INVENTION

Field of the Invention

The disclosed technique relates to an ophthalmic apparatus, aninformation processing method, and a storage medium.

Description of the Related Art

As a method for obtaining a tomographic image of a measurement object,such as a living body, in a non-destructive manner and a non-invasivemanner, optical coherence tomography (OCT) is used in practice. The OCTis widely used in ophthalmic diagnoses in particular.

In the OCT, light reflected by the measurement object and lightreflected by a reference mirror interfere with each other and anintensity of a resultant interference light is analyzed so that atomographic image of the measurement object is obtained. Examples ofsuch a light interference tomographic image obtaining apparatus includespectral domain optical coherence tomography (SD-OCT) which dividesinterference light and which replaces depth information by frequencyinformation to be obtained and swept source optical coherence tomography(SS-OCT) which divides wavelength first before outputting light. Notethat, the SD-OCT and the SS-OCT are collectively referred to as Fourierdomain optical coherence tomography (FD-OCT).

In recent years, an angiography method using the FD-OCT has beenproposed which is referred to as “OCT angiography”. U.S. PatentApplication Publication No. 2014/221827 discloses OCT angiography whichdetermines variation of logarithmic intensity of an interference signalas a motion contrast feature value and generates an image of the motioncontrast feature value.

However, U.S. Patent Application Publication No. 2014/221827 does notdisclose a method for specifying a blood vessel having a possibility ofa new blood vessel in an image of blood vessels obtained by imaging themotion contrast feature value.

SUMMARY OF THE INVENTION

A disclosed ophthalmic apparatus includes a generation unit configuredto generate 3D blood vessel data indicating a blood vessel in a fundusbased on a plurality of tomographic image data indicating cross sectionsof the fundus, a boundary obtaining unit configured to obtain layerboundary data indicating at least one layer boundary based on 3Dtomographic image data including the plurality of tomographic image dataindicating the cross sections of the fundus, and a determination unitconfigured to determine a blood vessel intersecting with the layerboundary by comparing the 3D blood vessel data with the layer boundarydata.

Further features of the present invention will become apparent from thefollowing description of exemplary embodiments with reference to theattached drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a diagram illustrating an entire configuration of an imagingapparatus.

FIG. 2 is a diagram illustrating a scanning pattern.

FIG. 3 is a flowchart illustrating a procedure of an obtainment of aninterference signal.

FIG. 4 is a flowchart illustrating a procedure of signal processing.

FIG. 5 is a flowchart illustrating a 3D blood vessel informationobtaining process.

FIG. 6 is a diagram illustrating a result of segmentation.

FIG. 7 is a diagram illustrating a display screen of a display unit.

FIG. 8 is a diagram illustrating a configuration of polarization OCT.

DESCRIPTION OF THE EMBODIMENTS

Hereinafter, an image generation apparatus according to an embodimentwill be described with reference to the accompanying drawings. Note thatconfigurations in embodiments below are merely examples, and the presentinvention is not limited to the embodiments.

First Embodiment Configuration of Entire Imaging Apparatus

A first embodiment will be described hereinafter with reference to theaccompanying drawings.

FIG. 1 is a diagram illustrating a configuration of an imaging apparatus(an OCT apparatus) employing optical coherence tomography according tothis embodiment. Although a configuration of the SS-OCT is illustratedin FIG. 1, the same effect may be realized by an OCT apparatus employingother methods.

This OCT apparatus (an ophthalmic apparatus) includes awavelength-sweeping light source 10, an optical signalbranching/multiplexing unit 20, an interference light detection unit 30,a computer 40 (the ophthalmic apparatus) which obtains information on aretina of a human eye 100, a measurement arm 50, and a reference arm 60.The computer 40 includes a central arithmetic operation unit (CPU) and astorage device. The storage unit includes memories (a RAM and a ROM) anda mass storage (HDD), for example. A portion of the storage device orthe entire storage device may be disposed outside the computer 40. Thewavelength-sweeping light source 10 emits light having a wavelength in arange from 980 nm to 1100 nm in a frequency of 100 kHz (an A scan rate),for example. Here, the wavelength and the frequency are merely examples,and the present invention is not limited to the values described above.Similarly, in the embodiments described below, described numericalvalues are merely examples, and the present invention is not limited tothe described numerical values.

Note that, although a human eye (a fundus) is set as an object 100 inthis embodiment, the present invention is not limited to this, and thepresent invention may be applied to a skin, for example. Furthermore,although the fundus is set as an imaging target in this embodiment, ananterior eye may be set as an imaging target.

The optical signal branching/multiplexing unit 20 includes couplers 21and 22. The coupler 21 divides light emitted from the light source 10into irradiation light to be emitted to a fundus and reference light.The irradiation light is emitted to the human eye 100 through themeasurement arm 50. Specifically, the irradiation light which enters themeasurement arm 50 is output from a collimator 52 as spatial light aftera polarization state of the irradiation light is adjusted by a polarizedlight controller 51. Thereafter, the irradiation light is emitted to thefundus of the human eye 100 through an x-axis scanner 53, a y-axisscanner 54, and a focus lens 55. The x-axis scanner 53 and the y-axisscanner 54 are included in a scanning unit having a function of scanninga fundus with irradiation light. The scanning unit changes a position ofirradiation with the irradiation light on the fundus. Here, a process ofobtaining information on a point of the human eye 100 in a depthdirection is referred to as “A scan”. Furthermore, a process ofobtaining a 2D tomographic image along a direction orthogonal to thedirection of the A scan is referred to as “B scan”, and a process ofobtaining a 2D tomographic image along a direction vertical to the 2Dtomographic image of the B scan is referred to as “C scan”.

Note that the x-axis scanner 53 and the y-axis scanner 54 are configuredby mirrors having rotation axes which are orthogonal to each other. Thex-axis scanner 53 performs scanning in an x direction and the y-axisscanner 54 performs scanning in a y direction. The x direction and the ydirection are vertical to an eye axis direction of an eyeball and arevertical to each other. Furthermore, directions of line scan, such asthe B scan and the C scan, may not coincide with the x direction or they direction. Therefore, line scan directions of the B scan and the Cscan may be appropriately determined in accordance with a 2D tomographicimage to be captured or a 3D tomographic image to be captured.

Reflection light from the fundus is incident on the coupler 22 throughthe coupler 21 after passing through the same path including the focuslens 55 again. Note that, if a measurement is performed in a state inwhich a shutter 85 is closed, a measurement of a background (noisefloor) may be performed while the reflection light from the human eye100 is cut.

On the other hand, the reference light is incident on the coupler 22through the reference arm 60. Specifically, the reference light whichenters the reference arm 60 is output from a collimator 62 as spatiallight after a polarization state of the reference light is adjusted by apolarized light controller 61. Thereafter, the reference light isincident on an optical fiber through a dispersion compensation glass 63,an optical path length control optical system 64, a dispersion controlprism pair 65, and a collimator lens 66, emitted from the reference arm60, and further incident on the coupler 22.

In the coupler 22, the reflection light of the human eye 100 transmittedthrough the measurement arm 50 and the reference light transmittedthrough the reference arm 60 interfere with each other. Resultantinterference light is detected by the detection unit 30. The detectionunit 30 includes a differential detector 31 and an A/D converter 32.First, the differential detector 31 of the detection unit 30 detects theinterference light divided by the coupler 22. Then the A/D converter 32converts an OCT interference signal (hereinafter simply referred to asan “interference signal” where appropriate) which has been convertedinto an electric signal by the differential detector 31 into a digitalsignal. Here, the differential detector 31 performs sampling of theinterference light at even wavenumber interval in accordance with a kclock signal generated by a clock generator incorporated in thewavelength-sweeping light source 10. The digital signal output from theA/D converter 32 is supplied to the computer 40. Subsequently, thecomputer 40 performs signal processing on the interference signal whichhas been converted into the digital signal so as to calculate an OCTangiography image. FIG. 7 is a diagram illustrating the OCT angiographyimage.

A CPU included in the computer 40 executes various processes.Specifically, the CPU executes programs stored in a storage device, notillustrated, so as to function as an obtaining unit 41, a positioningunit 42, a calculation unit 43, a generation unit 44, a determinationunit 45, and a display controller 46. The computer 40 includes at leastone CPU and at least one storage device. Specifically, at least oneprocessing unit (the CPU) and at least one storage device (a ROM, a RAM,or the like) are connected to each other, and the computer 40 functionsas the units described above when the at least one processing unitexecutes programs stored in the at least one storage device. Note thatthe processing unit is not limited to the CPU and may be afield-programmable gate array (FPGA) or the like. Furthermore, thecomputer 40 may be an apparatus which is integrated with a display unit70 and which is portable by a user (a tablet). In this case, the displayunit 70 may have a touch panel function which accepts various useroperations performed on a touch panel.

The obtaining unit 41 obtains an output from the A/D converter 32.Specifically, the obtaining unit 41 obtains the digital signal of theinterference light obtained from the measurement light which is returnedfrom an eye to be inspected and which is used for scanning on the eye tobe inspected and the reference light which interfere with each other.The obtaining unit 41 further obtains a tomographic image by performingFourier transform on the digital signal of the interference light (theinterference signal). Specifically, the obtaining unit 41 obtains an OCTcomplex signal formed by a phase and amplitude by performing fastFourier transform (FFT) on the interference signal. Note that a maximumentropy method may be used as frequency analysis. The obtaining unit 41further obtains a tomographic image indicating intensity (hereinaftersimply referred to as a “tomographic image” where appropriate) bycalculating square of an absolute value of the OCT complex signal so asto obtain a signal intensity (intensity). This tomographic imagecorresponds to an example of tomographic data indicating a layer of thefundus of the eye to be inspected. Specifically, in a case where thefundus of the eye to be inspected is scanned a plurality of times usingthe measurement light in substantially the same position, the obtainingunit 41 obtains a plurality of tomographic data indicating layers of thesubject in substantially the same position. Note that the plurality oftomographic data is obtained using the measurement light used inscanning operations performed in different timings. Furthermore, in acase where scanning is performed on a plurality of positions of thefundus using the measurement light, the obtaining unit 41 obtains aplurality of tomographic data in the plurality of positions.Specifically, the obtaining unit 41 corresponds to an example of firstand second obtaining units.

Note that the obtaining unit 41 also functions as a unit which controlsthe various units included in the OCT apparatus, such as the x-axisscanner 53 and the y-axis scanner 54.

The positioning unit 42 performs positioning of a plurality oftomographic images. In this embodiment, the positioning unit 42 performspositioning of a plurality of tomographic images obtained by performingscanning a plurality of times on the fundus of the eye to be inspectedusing the measurement light in substantially the same position. Morespecifically, the positioning unit 42 performs positioning of aplurality of tomographic data before the calculation unit 43 calculatesa motion contrast value.

The positioning of tomographic images may be realized by one of generalmethods. The positioning unit 42 performs positioning of the pluralityof tomographic images such that the correlation among the tomographicimages becomes maximum, for example. Note that the positioning is notrequired in a case where the subject is not moved unlike an eye.Furthermore, the positioning is not required if a high tracing functionis provided even in a case where the subject is an eye. That is,positioning of tomographic images by the positioning unit 42 is notessential.

The calculation unit 43 calculates a motion contrast feature value(hereinafter referred to as a “motion contrast value” whereappropriate). Here, the term “motion contrast” indicates contrastbetween a flowing tissue (such as a blood) and a nonflowing tissue, anda feature value representing the motion contrast is defined as the“motion contrast feature value”.

The motion contrast feature value is calculated based on a change ofdata of a plurality of tomographic images obtained by performingscanning a plurality of time using the measurement light insubstantially the same position. For example, the calculation unit 43calculates dispersion of signal intensities (luminance) of the pluralityof tomographic images which have been subjected to the positioning asthe motion contrast feature value. More specifically, dispersion ofsignal intensities in positions corresponding to the plurality oftomographic images which have been subjected to the positioning iscalculated as the motion contrast feature value. For example, signalintensity of an image of a blood vessel at a certain time point isdifferent from signal intensity of an image of the blood vessel atanother time point, and therefore, a dispersion value of a portioncorresponding to the blood vessel is larger than that of a portion inwhich flowing, such as a blood flow, is not detected. Specifically, themotion contrast value becomes large as a change in the subject among theplurality of tomographic data becomes large. Accordingly, the motioncontrast may be represented by generating an image based on thedispersion value. Note that the motion contrast feature value is notlimited to the dispersion value, and may be standard deviation, adifference value, a decorrelation value, or a correlation value. Notethat, although the calculation unit 43 uses the dispersion of signalintensities or the like, the motion contrast feature value may becalculated using dispersion of phases.

Furthermore, the calculation unit 43 generates an averaging image bycalculating an average value of the plurality of tomographic imageswhich have been subjected to the positioning. The averaging image is atomographic image obtained by averaging the signal intensities of theplurality of tomographic images. The averaging image may be referred toas an “intensity averaging image”. The calculation unit 43 compares asignal intensity of the averaging image with a threshold value. In acase where a signal intensity of a certain position of the averagingimage is smaller than the threshold value, the calculation unit 43 setsa motion contrast feature value obtained based on dispersion or the likein the certain position of the averaging image as a value different froma feature value indicating a blood vessel. In the case where the signalintensity of the averaging image is lower than the threshold value, forexample, the calculation unit 43 sets a motion contrast feature valueobtained based on the dispersion or the like as 0. Specifically, in acase where a representative value indicating the signal intensity islower than the threshold value, the calculation unit 43 sets a motioncontrast value as a value smaller than a motion contrast value obtainedin a case where the representative value indicating the signal intensityis equal to or higher than the threshold value. Note that thecalculation unit 43 may compare the signal intensity of the averagingimage with the threshold value before calculating the dispersion of thesignal intensities of the plurality of tomographic images as the motioncontrast feature value. In a case where the signal intensity of theaveraging image is lower than the threshold value, for example, thecalculation unit 43 calculates a motion contrast feature value of 0whereas in a case where the signal intensity of the averaging image isequal to or higher than the threshold value, the calculation unit 43calculates the dispersion of the signal intensities of the plurality oftomographic images as the motion contrast feature value.

Here, the feature value of 0 denotes a black portion denoted by areference numeral 71 in a 2D blood vessel image illustrated in FIG. 7.Note that the motion contrast feature value may not be 0 flat and may bea value near 0. On the other hand, in the case where the signalintensity of the averaging image is equal to or higher than thethreshold value, the calculation unit 43 maintains the motion contrastfeature value obtained based on the dispersion and the like.Specifically, the calculation unit 43 calculates the motion contrastvalue based on the plurality of tomographic image data and calculatesagain the motion contrast value based on a result of comparison betweenthe representative value indicating the signal intensity and thethreshold value.

Although the signal intensity of the averaging image (an average valueof the signal intensities) is used as a target of the comparison withthe threshold value, the highest value, the lowest value, a medianvalue, or the like of the signal intensities in the positionscorresponding to the plurality of tomographic images may be used as therepresentative value. Furthermore, instead of the comparison between thesignal intensities obtained from the plurality of tomographic imageswith the threshold value, the calculation unit 43 may compare a signalintensity of one tomographic image with the threshold value and controlthe motion contrast feature value.

The generation unit 44 generates 3D blood vessel information (3D bloodvessel data) based on the motion contrast feature value. Specifically,the generation unit 44 corresponds to an example of a generation unitwhich generates 3D blood vessel data indicating a blood vessel in thefundus based on the plurality of tomographic image data indicatinglayers of the fundus.

Specifically, the generation unit 44 compares the motion contrastfeature value with a threshold value so as to perform the regiondividing process of distinguishing a blood vessel region from otherregions. Furthermore, the generation unit 44 may perform a smoothingprocess on the motion contrast feature value before executing the regiondividing process. The smoothing process will be described in detaillater. Note that the 3D blood vessel information includes a 3D bloodvessel image. Specifically, the 3D blood vessel information indicatesthe 3D blood vessel image.

Furthermore, the generation unit 44 may generate 2D blood vesselinformation (2D blood vessel data) by performing projection orintegration on the 3D blood vessel information in a depth range in anarbitrary retina direction. The 2D blood vessel information includes a2D blood vessel image (an en-face blood vessel image). Specifically, the2D blood vessel information indicates a 2D blood vessel image. Thereference numeral 71 of FIG. 7 indicates an example of the 2D bloodvessel image.

Furthermore, the generation unit 44 may extract the depth range in thearbitrary retina direction from the 3D blood vessel information so as togenerate partial 3D blood vessel information.

Note that the depth range in the arbitrary retina direction may be setby an examiner (an operator). For example, candidates of a selectablelayer, such as layers from IS/OS to RPE and layers from RPE to BM aredisplayed in the display unit 70. Among the displayed candidates of thelayer, the examiner selects a certain layer. The generation unit 44 mayperform integration on the layer selected by the examiner in the retinadepth direction so as to generate 2D blood vessel information or partial3D blood vessel information.

Furthermore, the generation unit 44 obtains layer boundary dataindicating at least one layer boundary from the 3D tomographic imagedata including the plurality of tomographic image data. Specifically,the generation unit 44 corresponds to an example of a boundary obtainingunit which obtains layer boundary data indicating at least one layerboundary based on the 3D tomographic image data including the pluralityof tomographic image data indicating layers of the fundus. The layerboundary data is 3D data, for example. A method for detecting a layerboundary will be described in detail later.

Note that, in this embodiment, the 3D layer boundary data and the 3Dblood vessel data are obtained based on the same tomographic image data.Specifically, the generation unit 44 which is an example of the boundaryobtaining unit obtains layer boundary data indicating at least one layerboundary based on the 3D tomographic image data including the pluralityof tomographic image data indicating the layers of the fundus used inthe generation of the 3D blood vessel data.

The determination unit 45 determines a blood vessel which intersectswith the layer boundary by comparing the 3D layer boundary data with thelayer boundary data. Furthermore, the determination unit 45 maydetermine a blood vessel included in a certain range from the layerboundary by comparing the 3D layer boundary data with the layer boundarydata. Note that the determination unit 45 extracts a blood vessel whichis seen to be a new blood vessel. The process of the determination unit45 will be described in detail later.

The display controller 46 displays various information in the displayunit 70. Specifically, the display controller 46 displays the 3D bloodvessel image indicated by the 3D blood vessel information generated bythe generation unit 44 in the display unit 70. Furthermore, the displaycontroller 46 displays the blood vessel determined by the determinationunit 45 in the display unit 70 in a state in which the determined bloodvessel is distinguished from other blood vessels. The display controller46 may display a 2D blood vessel image in the display unit 70. Moreover,the display controller 46 may display the blood vessel determined by thedetermination unit 45 included in the 2D blood vessel image in thedisplay unit 70 in a state in which the determined blood vessel isdistinguished from other blood vessels. The display controller 46 maydisplay at least one of the 3D blood vessel image and the 2D bloodvessel image in the display unit 70. Specifically, the displaycontroller 46 corresponds to an example of a display controller whichdisplays at least one of the 3D blood vessel image indicated by the 3Dblood vessel data and the 2D blood vessel image obtained by performingthe integration on the 3D blood vessel data in the fundus depthdirection in the display unit and which displays the blood vesseldetermined by the determination unit in the display unit in a state inwhich the determined blood vessel is distinguished from other bloodvessels. Control performed by the display controller 46 will bedescribed in detail later.

A procedure of signal processing performed by the computer 40 will bedescribed in detail later.

The display unit 70 displays various information under control of thedisplay controller 46. The display unit 70 is a liquid crystal display,for example. Furthermore, the display unit 70 displays an OCTangiography image obtained as a result of the signal processingdescribed above.

Scanning Pattern

Next, a scanning pattern of this embodiment will be described withreference to FIG. 2.

In the OCT angiography, a change of the interference signal with timedue to blood flow is to be measured, and therefore, a plurality ofinterference signals repeatedly measured in substantially the sameportion at least twice are required. In FIG. 2, a Z axis denotes anaxial direction of the irradiation light emitted to the human eye 100 (adepth direction), and X and Y axes form a plane orthogonal to the Zaxis, that is, the X and Y axes correspond to a fundus plane direction.

In FIG. 2, y1 to yn denote B scan in different Y positions, and ndenotes the number of samples in a y scan direction. Furthermore, x1 toxp denote sample positions in an X scan direction, and p denotes thenumber of samples in the X scan direction included in the B scan.Moreover, Δx denotes an interval between adjacent X positions (an xpitch), and Δy denotes an interval between adjacent Y positions (a ypitch). In addition, m denotes the number of times the measurement isrepeatedly performed by the B scan in substantially the same portion.Here, an initial position (x1, y1) may be arbitrarily set by thecomputer 40.

In this embodiment, the OCT apparatus repeatedly performs the B scan mtimes in substantially the same portion, and performs a scan method ofmoving to y positions in n portions. Note that the repeat scan methodmay be a scan method of repeatedly performing A scan in substantiallythe same portion and moving to a next position for forming the B scan.

Here, if the number m of times the repeat scan is performed is large,the number of times the measurement is performed in the same portion isincreased, and therefore, detection accuracy of blood flow is improved.However, a long period of time is required for the scanning, andtherefore, there arise problems in that motion artifact is generated inan image due to a motion of an eye (an involuntary eye movement) duringthe scanning and a burden for an examinee is increased. In thisembodiment, 4 is set to m taking balance between the number m of timesthe repeat scan is performed and the number of times the scanning isperformed in the same position into consideration. Note that m may befreely changed in accordance with an A scan speed of the OCT apparatusand a moving amount of the human eye 100. Specifically, the number oftimes the repeat scan is performed is not limited to the value describedabove.

Furthermore, an image size in the x and y directions is determined byp×n. If the image size in the x and y directions is large, a large rangemay be scanned with the same measurement pitch. However, a long periodof time is required for the scanning and the problems in the motionartifact and a burden for a patient arise. In this embodiment, 300 isset to n and p taking balance between the image size and the scanningtime into consideration. Note that values of n and p above may beappropriately changed. Specifically, the image size is not limited tothe value described above.

Furthermore, in this embodiment, an x pitch and a y pitch are determinedas a half of a beam spot diameter of the irradiation light on thefundus, that is, 10 μm. Since the x pitch and the y pitch are determinedas a half of the beam spot diameter on the fundus, a high definitionimage may be generated. Even if the x pitch and the y pitch are smallerthan a half of the beam spot diameter on the fundus, definition of agenerated image is barely improved.

On the other hand, if the x pitch and the y pitch are larger than a halfof the beam spot diameter on the fundus, although definition isdegraded, an image in a large range may be obtained. The x pitch and they pitch may be freely changed in accordance with a clinical demand.

A scan range of this embodiment is determined as follows: 3 mm (p×Δx) inan x direction and 3 mm (n×Δy) in a y direction.

Procedure of Obtainment of Interference Signal

Next, an example of a procedure of an obtainment of an interferencesignal according to this embodiment will be described with reference toFIG. 3.

In step S109, the obtaining unit 41 assigns 1 to an index i of aposition yi illustrated in FIG. 2. Thereafter, in step S110, theobtaining unit 41 controls a driving mechanism, not illustrated, so asto move scanning positions of the x-axis scanner 53 and the y-axisscanner 54 to a coordinate (x1, yi) of FIG. 2. In step S119, theobtaining unit 41 initializes an index j of the number of times repeatmeasurement is performed in the B scan to 1.

In step S120, the x-axis scanner 53 and the y-axis scanner 54 performj-th B scan of the repeat measurement. Note that a range of the B scanis (x1, yi) to (xp, yi). Here, the wavelength-sweeping light source 10emits light in an A scan rate of 100 kHz, and the number p of samples inthe x scan direction of the B scan is 300, for example. Accordingly, anet B scan time (Δtb) is represented by Expression 1 below.

Δtb=(1/100 kHz)×300=3 ms   Expression 1

Furthermore, as represented by Expression 2, a time interval of therepeat measurement is a sum of the net B scan time Δtb and a preparationtime Δtp of the x-axis scanner 53. The preparation time Δtp is a periodof time in which scan positions of the x-axis scanner 53 and the y-axisscanner 54 are adjusted, for example. Assuming that Δtp is 1 ms,Expression 2 is obtained.

Δt=Δtb+Δtp=4 ms   Expression 2

Furthermore, an entire measurement time tm is represented by Expression3 using the number m of times repetition is performed and the number nof samples in the y scan direction.

tm=Δt*m*n=(Δtb+Δtp)*m*n   Expression 3

Since m is 4 and y is 300 in this embodiment, the entire measurementtime tm is 3.6 s.

Here, as the B scan time Δtb and a time interval Δt of the repeatmeasurement are small, influence of a motion of the human eye 100 issmall and bulk motion noise is small. On the other hand, the timeinterval Δt is long, positional reproducibility is degraded due to amotion of the human eye 100, and accordingly, the bulk motion noise isincreased. Furthermore, a period of time required for the measurement isincreased, and a burden for the patient is increased. Here, the bulkmotion means a motion of the eye to be inspected, and the bulk motionnoise means noise generated due to a motion of the eye to be inspected.

Furthermore, if the time interval Δt of the repeat measurement is toosmall, a period of time required for detection of a blood flow is short,and accordingly, blood flow detection sensitivity is degraded.

Therefore, tm, Δt, n, p, Δtb, and Δtp are preferably selected takingthese elements into consideration. Note that, to enhance the positionalreproducibility of the repeat measurement, the x-axis scanner 53 and they-axis scanner 54 may perform the B scan while tracing the human eye100.

In step S130, the differential detector 31 detects the interferencelight for each A scan, and the interference light is converted into adigital signal (an interference signal) through the A/D converter 32.The obtaining unit 41 obtains the interference signal from the A/Dconverter 32 and stores the interference signal in a storage unit, notillustrated. The obtaining unit 41 obtains p A scan signals per one Bscan. The p A scan signals corresponds to one B scan signal.

In step S139, the obtaining unit 41 increments the index j of the numberof times the repeat measurement of the B scan is performed.

In step S140, the obtaining unit 41 determines whether the index j ofthe number of times the repeat measurement is performed is larger than apredetermined repeat number m. Specifically, the obtaining unit 41determines whether the B scan is repeatedly performed m times in theposition yi. When the determination is negative in step S140, theprocess returns to step S120 where the B scan measurement in the sameposition is performed again. When the determination is affirmative instep S140, the process proceeds to step S149.

In step S149, the obtaining unit 41 increments the index i of theposition yi.

In step S150, the obtaining unit 41 determines whether the index i ofthe position yi is larger than the predetermined number n of measurementpositions, that is, whether the B scan has been performed in all Ypositions in n portions. When the determination is negative, the processreturns to step S110 so that an operation of performing the measurementin a next measurement position is performed again. On the other hand,when the determination is affirmative, the process proceeds to stepS160.

In step S160, the obtaining unit 41 obtains background data. Theobtaining unit 41 controls a driving unit, not illustrated, so as toperform the A scan 100 times in a state in which the shutter 85 isclosed, averages 100 A scan signals, and stores a resultant value in astorage unit. Note that the number of times A scan is performed forobtaining the background data is not limited to 100.

The obtaining unit 41 may obtain the plurality of interference signalsobtained by performing the repeat measurement at least twice insubstantially the same portion and the background data.

Signal Processing Procedure

Next, an example of the signal processing procedure (an informationprocessing method) according to this embodiment will be described withreference to FIG. 4.

FIG. 4 is a flowchart illustrating a flow from an obtainment ofinterference signals to display of a 3D blood vessel image.

In this embodiment, a motion contrast feature value is required to becalculated to generate an OCT angiography image.

In step S210 of FIG. 4, the obtaining unit 41 sets the index i of theposition yi in the y direction as 1. In step S220, the obtaining unit 41extracts (m) B scan interference signals obtained by the B scanrepeatedly performed from the interference signals obtained by theprocess illustrated in FIG. 3 stored in the storage unit. Specifically,the obtaining unit 41 reads a plurality of B scan interference signalsobtained by the repeat B scan in the position yi from the storage unit.

In step S230, the obtaining unit 41 sets the index j of the repeat Bscan as 1.

In step S240, the obtaining unit 41 extracts a j-th B scan interferencesignal from the m B scan interference signals.

In step S250, the computer 40 subtracts the background data obtained instep S160 of FIG. 3 from the B scan interference signal obtained in stepS240.

In step S260, the obtaining unit 41 performs Fourier transform on the Bscan interference signal from which the background data is subtracted.In this embodiment, fast Fourier transform (FFT) is employed.

In step S270, the obtaining unit 41 calculates a square of an absolutevalue of amplitude of the B scan interference signal subjected to theFourier transform in step S260. A resultant value indicates an intensityof a B scan tomographic image. Specifically, the obtaining unit 41obtains a tomographic image indicating an intensity in step S270.

In step S280, the obtaining unit 41 increments the number j of times therepeat measurement is performed indicating the number of times the Bscan is repeatedly performed. In step S290, the obtaining unit 41determines whether the number j of times the repeat measurement isperformed is larger than the number m of times the repeat is performed.Specifically, the obtaining unit 41 determines whether an intensitycalculation of the B scan is repeatedly performed m times in theposition yi. When the number j of times the repeat measurement isperformed is smaller than the number m of times the repeat is performed,the process returns to step S240 where the obtaining unit 41 repeatedlyperforms an intensity calculation of the B scan in the same Y position.When the number j of times the repeat measurement is performed is largerthan the number m of times the repeat is performed, the process proceedsto step S300.

In step S300, the positioning unit 42 performs positioning ontomographic images for m frames of the repeat B scan in the certain Yposition yi. Specifically, the positioning unit 42 selects an arbitraryone of the tomographic images for the m frames as a template. Thepositioning unit 42 calculates the correlation among all combinations ofthe tomographic images of m frames, obtains a sum of correlationcoefficients for each frame, and selects a tomographic image of a framecorresponding to the largest sum as a template.

Thereafter, the positioning unit 42 compares the tomographic imageselected as the template with a tomographic image in another frame so asto obtain positional shift amounts (δX, δY, δθ). Specifically, thepositioning unit 42 calculates normalized cross-correlation (NCC) whichis an index of similarity between the template image and the tomographicimage of the other frame by changing a position and an angle of thetemplate image. Then the positioning unit 42 obtains a differencebetween the positions of the images corresponding to a largest value ofthe NCC as a positional shift amount. Note that, in the presentinvention, any criterion may be used as the index of the similarity aslong as similarity between a feature of the tomographic image selectedas the template and a feature of the tomographic image of the otherframe is indicated. For example, a sum of absolute difference (SAD), asum of squared difference (SSD), zero-means normalized cross-correlation(ZNCC), phase only correlation (POC), rotation invariant phase onlycorrelation (RIPOC), or the like may be used as the index indicating thesimilarity.

The positioning unit 42 performs positioning of the tomographic imagesfor the m frames in accordance with the positional shift amounts (δX,δY, δθ) while applying position correction of a tomographic imageindicating intensity to the tomographic images for (m−1) frames otherthan the template. After the positioning is completed, a process in stepS310 and step S311 is performed.

In step S310, the calculation unit 43 calculates a motion contrastfeature value. In this embodiment, the calculation unit 43 calculates adispersion value for each pixel in the same position of the tomographicimages for the m frames which are subjected to the positioning in stepS300, and the dispersion value is determined as the motion contrastfeature value. Note that various methods for obtaining the motioncontrast feature value may be employed as long as an index indicates achange of a luminance value of pixels in the same Y position in aplurality of tomographic images.

On the other hand, in step S311, the calculation unit 43 calculates anaverage of the m tomographic images (intensity images) which areobtained in step S300 and which have been subjected to the positioningso as to generate an intensity averaging image.

In step S330, the obtaining unit 41 increments the index i of theposition yi. In step S340, the obtaining unit 41 determines whether theindex i is larger than the number n of measurement points. Specifically,the obtaining unit 41 determines whether the positioning, thecalculation of the intensity averaging image, and the calculation of themotion contrast feature value have been performed in all the n Ypositions. When the index i is equal to or smaller than the number n ofthe measurement positions, the process returns to step S220 whereas whenthe index i is larger than the number n of the measurement positions,the process proceeds to step S350 and step S360.

At a time when the process in step S340 is terminated, the intensityaveraging images and 3D volume data of the motion contrast featurevalues of individual pixels of the tomographic images (Z-X plane) in allthe Y positions have been obtained.

After the process in step S340 is terminated, the process proceeds tostep S350 and step S360. A 3D blood vessel information obtaining processis executed in step S350, and a retina layer segmentation process isexecuted in step S360. These processes may be executed in parallel orsuccessively executed. Note that the process in step S360 may beexecuted after the process in step S350 and vice versa.

First, the 3D blood vessel information obtaining process in step S350will be described. Here, a procedure of a process of obtaining 3D bloodvessel information from 3D volume data of a motion contrast featurevalue will be described as an example.

FIG. 5 is a flowchart illustrating the process in step S350 of FIG. 4 indetail.

In step S351, the generation unit 44 obtains the 3D volume data of themotion contrast feature value which has been obtained.

In step S352, the generation unit 44 performs a smoothing process on the3D volume data of the motion contrast feature value so as to removenoise while blood vessel information remains.

Although the most appropriate smoothing process is changed depending ona type of the motion contrast feature value, the following smoothingprocess may be used, for example.

(1) Smoothing method for outputting the largest value of the motioncontrast feature values from (nx×ny×nz) voxels in the vicinity of atarget pixel (n is an arbitrary number).

(2) Smoothing method for outputting an average value of the motioncontrast feature values in the (nx×ny×nz) voxels in the vicinity of thetarget pixel. A median value may be output instead of the average value.

(3) Smoothing method for weighting the motion contrast feature values inthe (nx×ny×nz) voxels in the vicinity of the target pixel bycorresponding distances. In this smoothing method, the larger a distancefrom the target pixel becomes, the lower the weighting becomes.Furthermore, since a target blood vessel intersects with a layerboundary, weighting is increased in a depth direction, for example, asthe weighting method based on distances. Specifically, even if twopixels are positioned in the same distance from the target pixel, one ofthe pixels positioned in the depth direction is highly weighted whencompared with the other of the pixels positioned in a directionorthogonal to the depth direction.

(4) Smoothing method for applying weight depending on distances anddepending on differences from a pixel value of the target pixel to themotion contrast feature values in the (nx×ny×nz) voxels in the vicinityof the target pixel. The smaller the difference between pixel valuesbecomes, the larger the weighting becomes, for example.

(5) Smoothing method for outputting a value using weighting depending onsimilarity between a pattern of a motion contrast feature value in asmall region surrounding the target pixel and a pattern of a motioncontrast feature value in a small region surrounding a peripheral pixel.In this smoothing method, the higher the similarity is, the larger theweighting is.

Note that the smoothing may be performed while blood vessel informationremains. Furthermore, the smoothing process is not essential and may beomitted.

In step S353, the generation unit 44 performs the region dividingprocess of distinguishing a blood vessel from other regions on the 3Dvolume data of the motion contrast feature value which has beensubjected to the smoothing process.

As the region dividing process, a method for determining a region havinga voxel value indicating a motion contrast feature value equal to orsmaller than a threshold value as a region other than a blood vessel,for example, may be employed. Here, an adaptive threshold setting may beperformed by calculating weighted average in a mx×my×mz region in thevicinity of the target pixel and subtracting a constant number from aresultant value so that a threshold values is set for each pixel. Notethat the constant number may be defined as several % of the weightedaverage. Furthermore, m is an arbitrary number. The threshold value maybe a fixed value.

Furthermore, in the region dividing process using the threshold value,the generation unit 44 may binarize blood vessels and other regions. Inthis case, the generation unit 44 may perform a closing (expansion toshrinkage) process and an opening (shrinkage to expansion) process onthe 3D volume data which has been subjected to the binarizing processingso as to remove noise.

Furthermore, the generation unit 44 may employ a method for determininga cost function which obtains a smallest cost when labeling isappropriately performed on regions of blood vessels and other regionsand obtaining a combination of the labels corresponding to the smallestcost in the 3D volume data of the motion contrast feature value.Specifically, the generation unit 44 may employ a graph cut method, forexample.

Note that other region dividing processing methods may be employed.

By the process described above, the 3D blood vessel information isobtained from the 3D volume data of the motion contrast feature value.In addition to the determination as to whether the individual pixelscorrespond to a blood vessel performed as described above, the number ofpixels which are determined to correspond to a blood vessel and whichare consecutively arranged may be taken into consideration. For example,the generation unit 44 may determine, in the pixels determined tocorrespond to a blood vessel, a portion in which the number of pixelsdetermined to correspond to a blood vessel is equal to or larger than apredetermined value as a blood vessel and a portion in which the numberof pixels determined to correspond to a blood vessel is smaller than thepredetermined value as a portion which does not correspond to a bloodvessel. Furthermore, the generation unit 44 determines continuity of thepixels determined as a blood vessel so as to detect at least one of anextending direction of the blood vessel, a length of the blood vessel,and ends of the blood vessel.

Here, as the retina layer segmentation process in step S360, asegmentation process using the intensity averaging image generated instep S311 will be described in detail.

The generation unit 44 extracts an intensity averaging image to beprocessed from among the intensity averaging images in the plurality ofY positions. The generation unit 44 applies a median filter and a Sobelfilter to the extracted intensity averaging image so as to generaterespective images (hereinafter individually referred to as a “medianimage” and a “Sobel image”).

Subsequently, the generation unit 44 generates profiles for each A scanusing the generated median image and the generated Sobel image. Aprofile of a luminance value is generated using the median image and aprofile of gradient is generated using the Sobel image. The generationunit 44 detects a peak in the profile generated using the Sobel image.The generation unit 44 extracts a boundary (a layer boundary) betweenregions of the retina layer with reference to a profile of the medianimage corresponding to a portion before and after the peak detected inthe Sobel image or a profile of the median image corresponding to aportion between peaks. Specifically, the generation unit 44 obtainslayer boundary data indicating a layer boundary.

FIG. 6 is a diagram illustrating a result of the segmentation. FIG. 6 isa diagram illustrating the intensity averaging image in the Y position,and segmentation lines (layer boundaries) denoted by dotted linesoverlaid on the intensity averaging image. In the segmentation processof this embodiment, a boundary between a nerve fiber layer (NFL) and alayer of a combination of a ganglion cell layer (GCL) and an innerplexiform layer (IPL) is detected. Furthermore, a boundary between alayer of a combination of an ellipsoid zone (EZ), an interdigitationzone (IZ), and a retinal pigment epithelium (RPE) and a choroid layerand so on are detected. Note that layer boundaries to be detected arenot limited to the examples described above, and the generation unit 44may detect at least one of a boundary between a Bruch membrane and aretinal pigment epithelium layer and a boundary between the Bruchmembrane and a choroid layer, for example. Note that the generation unit44 obtains layer boundary data indicating coordinates of a detectedlayer boundary or the like. Specifically, the layer boundary dataindicates at least one of the boundary between the Bruch membrane andthe retinal pigment epithelium layer and the boundary between the Bruchmembrane and the choroid layer. The generation unit 44 may obtain 3Dlayer boundary data by performing the process described above on theintensity averaging images in the plurality of Y positions.

The segmentation process of this embodiment is merely an example, andother methods may be employed such as a segmentation process using aDijkstra method. Furthermore, the number of layers to be detected may bearbitrarily set.

In step S370, the determination unit 45 determines (extracts) a bloodvessel which intersects with a layer boundary based on the 3D bloodvessel information obtained in step S350 and the layer boundary dataobtained in step S360. Specifically, the determination unit 45determines a blood vessel which intersects with the layer boundary as anew blood vessel. Specifically, the determination unit 45 comparescoordinates of the blood vessel included in the 3D blood vesselinformation with coordinates of the layer boundary included in the layerboundary data, for example, so as to specify the blood vessel having acoordinate the same as that of the layer boundary as a blood vesselintersecting with the layer boundary. Furthermore, in a case where acoordinate in a depth direction of the layer boundary is includedbetween coordinates of opposite ends of the blood vessel in the depthdirection obtained by the generation unit 44, the determination unit 45may specify the blood vessel as a blood vessel intersecting with thelayer boundary. The determination unit 45 may specify, in a case where acoordinate of an end of the blood vessel obtained by the generation unit44 matches a coordinate of the layer boundary, the blood vessel as ablood vessel intersecting with the layer boundary. Specifically, thedetermination unit 45 determines at least one of a blood vesselintersecting with a layer boundary and a blood vessel which is incontact with the layer boundary.

Here, in a case where the 3D blood vessel information and the layerboundary are obtained from different tomographic image data, positioningis performed on the different tomographic image data so that coordinatesof pixels determined as a blood vessel included in the 3D blood vesselinformation is compared with coordinates of the layer boundary. Thepositioning of the different tomographic image data is realized bypositioning of integrated images obtained based on individualtomographic images corresponding to the different tomographic imagedata, for example. In a case where the 3D blood vessel information andthe layer boundary are obtained from the same tomographic image data,the positioning described above may be omitted.

Although a blood vessel intersecting with a layer boundary is seen to bea new blood vessel in the example described above, a blood vessel, amongvarious blood vessels, included in a predetermined range from the layerboundary may be determined as a new blood vessel. This is because ablood vessel included in the predetermined range from the layer boundarymay be a new blood vessel. Although a layer boundary surface of theretina layer is uniquely determined by calculation, the boundary isfuzzy in practice, and a boundary may be broken particularly in anaffected eye, and accordingly, the determination unit 45 determineswhether a blood vessel is included in the predetermined range from thelayer boundary surface, that is, in the vicinity of the layer boundary.The determination unit 45 determines, in a case where a coordinate of anend of the blood vessel obtained by the generation unit 44 is includedin a predetermined range from the coordinate of the layer boundary, theblood vessel is determined to be included in the predetermined rangefrom the layer boundary.

Note that the determination unit 45 may take an angle of a blood vesselinto consideration so as to more reliably determine a new blood vessel.This is because a characteristic that a new blood vessel extends in adirection of a surface of the retinal is utilized. The determinationunit 45 may determine a blood vessel which is positioned within thepredetermined range from the layer boundary and which has an angle in arange from 45 degrees to 135 degrees relative to a horizontal directionas a new blood vessel. Note that the angle described above is merely anexample, and any value may be employed as long as a blood vesselextending in the direction of the surface of the retina is extracted.The determination unit 45 may determine, as with the case describedabove, a new blood vessel taking an angle of a blood vessel intoconsideration even in the case where the blood vessel intersects withthe layer boundary.

Note that the determination unit 45 may take a length of a blood vesselinto consideration so as to more reliably determine a new blood vessel.This is because an inappropriate determination in which noise which isnot a blood vessel is mistakenly determined as a blood vessel is to beavoided. The determination unit 45 may determine a blood vessel which ispositioned within the predetermined range from the layer boundary andwhich has an angle in a range from 45 degrees to 135 degrees relative toa horizontal direction as a new blood vessel, for example. Thedetermination unit 45 may determine, as with the case described above, anew blood vessel taking a length of a blood vessel into considerationeven in the case where the blood vessel intersects with the layerboundary.

Note that the determination unit 45 may determine a new blood vesseltaking all the positional relationship between a layer boundary and ablood vessel, and an angle of the blood vessel, and a length of theblood vessel into consideration. Furthermore, the determination unit 45may determine a new blood vessel only based on an angle of a bloodvessel. Moreover, the determination unit 45 may determine a new bloodvessel based on an angle and a length of a blood vessel.

Note that the determination unit 45 may assign, to a blood vessel,reliability indicating that the blood vessel is a new blood vessel. Forexample, the determination unit 45 assigns higher reliability to a bloodvessel intersecting with a layer boundary when compared with a bloodvessel included in the predetermined range from the layer boundary. Onthe other hand, the determination unit 45 assigns lower reliability to ablood vessel included in the predetermined range from the layer boundarywhen compared with a blood vessel intersecting with the layer boundary.The assignment of the reliability is realized by setting a flag to bloodvessel information based on the reliability. The determination unit 45may assign higher reliability as a blood vessel is positioned nearer toa layer boundary. Furthermore, the determination unit 45 may assignhigher reliability as an angle of a blood vessel is close to vertical.The determination unit 45 may assign higher reliability as a bloodvessel is longer. Furthermore, the determination unit 45 may assignhigher reliability to a blood vessel intersecting with a layer boundarywhen compared with a blood vessel which is in contact with the layerboundary. Furthermore, the determination unit 45 may assign higherreliability to a blood vessel intersecting with a layer boundary as theblood vessel is longer. Moreover, in a case where a blood vesselintersects with a layer boundary, the determination unit 45 may assignhigher reliability to the blood vessel as the blood vessel which extendsfrom an intersection between the layer boundary and the blood vesseltoward the surface of the retina is longer. Although the reliability isassigned in the examples described above, the reliability may bereplaced by a growth degree of a new blood vessel. The high reliabilitymay be replaced by a high growth degree (large growth of a new bloodvessel).

In step S380, the display controller 46 displays a blood vessel imagebased on the 3D blood vessel information in the display unit 70. FIG. 7is a diagram illustrating a display screen of the display unit 70. Asillustrated in FIG. 7, the display controller 46 displays a 2D bloodvessel image 71, a tomographic image 72, and a 3D blood vessel image 73in the display unit 70. Furthermore, the display controller 46 displayslayer boundaries obtained by the generation unit 44 in the 3D bloodvessel image 73 in an overlapping manner in the display unit 70.Specifically, the display controller 46 displays the layer boundariesindicated by the layer boundary data on the 3D blood vessel image 73 inan overlapping manner in the display unit. Note that the displaycontroller 46 may display names of layers positioned on and below thelayer boundaries so as to clearly display positions of the displayedlayer boundaries.

Furthermore, the display controller 46 displays, in the display unit 70,a blood vessel determined by the determination unit 45 and other bloodvessels such that the blood vessel determined by the determination unit45 is distinguished from the other blood vessels. In the example of FIG.7, the display controller 46 displays, in the display unit 70, arrowmarks indicating blood vessels determined by the determination unit 45.Furthermore, the display controller 46 displays circles indicatingportions intersecting with a layer boundary in the display unit 70.Specifically, the display controller 46 displays a blood vessel imagebased on 3D blood vessel data in the display unit and further displaysan object indicating a blood vessel determined by the determination unitin the display unit. Here, the circles are examples of the object. Aform of the object is not limited to a circle.

The display controller 46 displays the blood vessel determined by thedetermination unit 45 and the other blood vessels in a distinguishablemanner using the arrow marks and the circles in the display unit 70. Adisplay form indicating the blood vessel determined by the determinationunit 45 is not limited to the example of FIG. 7. An end of a bloodvessel included in the predetermined range from the layer boundary maybe emphasized by the circle as illustrated in FIG. 7. Moreover, thedisplay controller 46 may display the blood vessel determined by thedetermination unit 45 by a color different from a color of the otherblood vessels in the display unit 70. The display controller 46 maydisplay the blood vessel determined by the determination unit 45 by redand the other blood vessels by white, for example, in the display unit70. The number of colors is not limited. Specifically, the displaycontroller 46 displays a blood vessel image based on 3D blood vesseldata in the display unit and further displays a blood vessel determinedby the determination unit by a color different from a color of the otherblood vessels in the display unit.

Furthermore, in a case where the reliability (or the growth degree) isassigned to a blood vessel, the display controller 46 may display theblood vessel in the display unit 70 in a display form changed dependingon the reliability. For example, the display controller 46 may display ablood vessel in a color closer to red as the reliability becomes higherin the display unit 70, and display a blood vessel in a color similar towhite (closer to a display color of the other blood vessels) as thereliability becomes lower.

Moreover, the display controller 46 may display blood vessels determinedby the determination unit relative to all the detected layer boundaries45 in the display unit 70 in the display form described above.Specifically, boundary data indicates a plurality of layer boundaries.Furthermore, the display controller 46 may display the blood vesseldetermined by the determination unit 45 relative to only an arbitrarylayer boundary selected from among the plurality of layer boundaries bythe user in the display unit 70 in the display form described above.Specifically, the determination unit 45 determines a blood vesselintersecting with a layer boundary selected from among the plurality oflayer boundaries.

Note that the selection of a layer boundary performed by the user isrealized as described below, for example. The display controller 46displays a result of detection of a layer boundary on the tomographicimage 72 in an overlapping manner in the display unit 70, and the userselects a target layer boundary from among a plurality of displayedlayer boundaries by clicking, tapping, or the like. Specifically, thedisplay controller 46 displays a 2D tomographic image based on 3Dtomographic image data in the display unit and further displays theplurality of layer boundaries on the 2D tomographic image in anoverlapping manner. Thereafter, in a case where one of the layerboundaries displayed on the 2D tomographic image in an overlappingmanner is selected, the determination unit 45 determines a blood vesselintersecting with the layer boundary selected from among the pluralityof layer boundaries.

Note that a new blood vessel intersects with the layer boundary betweenthe choroid layer and the Bruch membrane and/or the layer boundarybetween the Bruch membrane and the retinal pigment epithelium layer, forexample. Here, the display controller 46 may display, in the displayunit 70, the blood vessel intersecting with the layer boundary betweenthe choroid layer and the Bruch membrane and/or the layer boundarybetween the Bruch membrane and the retinal pigment epithelium layer in adisplay form different from that of the other blood vessels when thescreen illustrated in FIG. 7 is entered. Specifically, in a defaultstate of display in FIG. 7, the layer boundary between the choroid layerand the Bruch membrane and/or the layer boundary between the Bruchmembrane and the retinal pigment epithelium layer may be automaticallyselected from among the plurality of layer boundaries.

Note that the display controller 46 may display the blood vesseldetermined by the determination unit 45 such that the blood vesseldetermined by the determination unit 45 is distinguished from the otherblood vessels. Furthermore, the display controller 46 may display afundus image in the display unit 70, and display arrow marks, circles,and the like indicating a position of a blood vessel of the fundusdetermined by the determination unit 45 in an overlapping manner. Notethat the fundus image may be obtained by integrating tomographic imagesor obtained by a fundus camera or the SLO. Positioning of the 3D bloodvessel image and the fundus image is realized by positioning of anintegrated image obtained from the tomographic image data which is abase of the 3D blood vessel image and the fundus image. Specifically,positioning of the 3D blood vessel image and the fundus image isperformed using the tomographic image data. Accordingly, the displaycontroller 46 may display the arrow marks, the circles, and the likeindicating a position of the blood vessel determined by thedetermination unit 45 on the fundus image in an overlapping manner inthe display unit 70.

Note that the display controller 46 may not display all the 2D bloodvessel image 71, the tomographic image 72, and the 3D blood vessel image73 in the display unit 70 and may display an arbitrary image orarbitrary images in the display unit 70. For example, the displaycontroller 46 may display only the 3D blood vessel image 73 on which thelayer boundaries are superposed in the display unit 70 in a state inwhich the blood vessel determined by the determination unit 45 isdistinguished from the other blood vessels.

As described above, according to this embodiment, a blood vessel whichis a possible new blood vessel may be specified. Furthermore, the bloodvessel determined as the new blood vessel is displayed such that the newblood vessel is distinguished from the other blood vessels so that theuser, such as a doctor, may easily and swiftly recognize the bloodvessel which is a possible new blood vessel. Furthermore, in a defaultstate in which blood vessel images are displayed, a blood vesselintersecting with the layer boundary between the choroid layer and theBruch membrane and/or the layer boundary between the Bruch membrane andthe retinal pigment epithelium layer where a new blood vessel is highlylikely to be generated are displayed in a state in which the bloodvessel is distinguished from the other blood vessels. Accordingly, theuser, such as a doctor, may swiftly recognize the blood vessel which isa possible new blood vessel.

Furthermore, according to this embodiment, a blood vessel is displayedin the display form based on reliability, and therefore, this displayassists a determination as to whether the blood vessel is actually a newblood vessel made by the user, such as a doctor. Furthermore, accordingto this embodiment, a blood vessel is displayed in the display formbased on a growth degree, and therefore, the user, such as a doctor, mayswiftly recognize a degree of disease with ease.

Furthermore, according to this embodiment, 3D blood vessel image and alayer boundary are obtained based on the same tomographic image data,and therefore, the positional relationship between the 3D blood vesselimage and the layer boundary may be easily recognized.

Although 3D layer boundary data and 3D blood vessel data are obtainedbased on the same tomographic image data according to this embodiment,the present invention is not limited to this. A plurality of tomographicimage data indicating the layers of the fundus to be used in thegeneration of 3D blood vessel data may be different from a plurality oftomographic image data indicating the layers of the fundus included inthe 3D tomographic image data to be used in an obtainment of layerboundary data. Furthermore, angles of view of the plurality oftomographic image data indicating the layers of the fundus to be used ingeneration of the 3D blood vessel data may be smaller than those of theplurality of tomographic image data indicating the layers of the fundusincluded in the 3D tomographic image data to be used in an obtainment ofthe layer boundary data. Specifically, the tomographic image data forobtaining the 3D layer boundary data may have an angle of view largerthan that of the tomographic image data in the foregoing embodiment sothat the user, such as a doctor, determines a range in the fundus toobtain the 3D blood vessel data.

Note that the scanning performed a plurality of times in substantiallythe same position is not required when tomographic image data having alarge angle of field is to be obtained. In a case where the tomographicimage data of large angle of field is obtained, the generation unit 44may obtain 3D layer boundary data from the tomographic image data of thelarge angle of view. Specifically, the 3D layer boundary data may beobtained from tomographic image data different from tomographic imagedata from which 3D blood vessel data is obtained.

Although the 3D blood vessel data and the 3D layer boundary data areused in the foregoing embodiments, the present invention is not limitedto this and 2D blood vessel data and 2D layer boundary data may be used.Even if the 2D data is used, a blood vessel intersecting with a layerboundary may be specified, and accordingly, the same effect of theforegoing embodiment may be attained.

Second Embodiment Configuration of Entire Imaging Apparatus

A case where a polarization OCT is used will be described in a secondembodiment. According to the polarization OCT, a tomographic image fromwhich a retinal pigment epithelium layer which cancels polarization maybe easily extracted may be obtained. Therefore, in this embodiment, theophthalmic apparatus detects a layer boundary between the retinalpigment epithelium layer and a Bruch membrane or the like and determinesa blood vessel and the like which intersects with the detected layerboundary as a new blood vessel. Specifically, this embodiment isdifferent from the first embodiment in a method for detecting a layerboundary. Note that a scanning pattern and so on which are notparticularly mentioned are the same as those of the first embodiment,and descriptions thereof are omitted.

FIG. 8 is a diagram illustrating the ophthalmic apparatus according tothis embodiment.

The ophthalmic apparatus includes polarization sensitive OCT (PS-OCT)1000 and a computer 200. Note that the computer 200 is substantially thesame as the computer 40 of the first embodiment except for somefunctions. Specifically, 3D tomographic image data is obtained by thePS-OCT 1000.

Configuration of PS-OCT 1000

A configuration of the PS-OCT 1000 will be described.

A light source 101 is an super luminescent diode (SLD) light sourcewhich is a low coherent light source, and emits light having a centralwavelength of 850 nm and a bandwidth of 50 nm, for example. Although theSLD is used as the light source 101, any light source may be used aslong as low coherent light is emitted, such as an amplified spontaneousemission (ASE) light source.

The light emitted from the light source 101 is transmitted through asingle mode (SM) fiber 134, a polarization controller 103, a connector135, and a polarization maintaining (PM) fiber 102. The light emittedfrom the light source 101 is further guided to a fiber coupler 104having a polarization maintaining function which divides the light intomeasurement light (or OCT measurement light) and reference light (orreference light corresponding to the OCT measurement light).

The polarization controller 103 controls a state of polarization of thelight emitted from the light source 101 so as to obtain linearlypolarized light. A division rate of the fiber coupler 104 is 90(reference light) to 10 (measurement light).

The divided measurement light is transmitted through a PM fiber 105 andemitted from a collimator 106 as parallel light. The emitted measurementlight is transmitted through an X scanner 107 configured by a Galvanomirror which scans the measurement light in a horizontal direction in afundus Er, a lens 108, and a lens 109. Furthermore, the emittedmeasurement light is transmitted through a Y scanner 110 configured by aGalvano mirror which performs scanning using the measurement light in avertical direction in the fundus Er to a dichroic mirror 111. The Xscanner 107 and the Y scanner 110 are controlled by an obtaining unit 41and may scan a desired range of the fundus Er (a range in which atomographic image is to be obtained, a position where a tomographicimage is to be obtained, or a position emitted by the measurement light)with the measurement light. The dichroic mirror 111 has a characteristicin which light having a wavelength of 800 nm to 900 nm is reflected andother light is transmitted.

The measurement light reflected by the dichroic mirror 111 istransmitted through a lens 112 and a λ/4 polarizing plate 113 (anexample of a polarization control member) which is disposed with aninclination of 45 degrees in an in-plane which is vertical to an opticalaxis of the measurement light so that a phase of the measurement lightis shifted by 90 degrees, and accordingly, polarization control isperformed so that circularly polarized light is obtained. Note that theinclination of the λ/4 polarizing plate 113 preferably has an angle (anexample of an arrangement state) corresponding to an inclinationrelative to an optical axis of a polarization division plane of a fibercoupler 123 incorporating a polarizing beam splitter, for example.

Note that the λ/4 polarizing plate 113 is preferably detachable from alight path. For example, a mechanical configuration in which an axiswhich is parallel to an optical axis is used as a rotation axis forrotation of the λ/4 polarizing plate 113 may be employed. By this, asmall apparatus capable of easily performing switching between an SLOoptical system and a PS-SLO optical system may be realized. Furthermore,a small apparatus capable of easily performing switching between an OCToptical system and a PS-OCT optical system may be realized.

Although light to be incident on an eye to be inspected is subjected tothe polarization control by the λ/4 polarizing plate 113 which isdisposed on the in-plane which is vertical to the optical axis of themeasurement light in a state in which the λ/4 polarizing plate 113 isinclined by 45 degrees so that circularly polarized light is obtained,the circularly polarized light may not be obtained in the fundus Er dueto a characteristic of the eye to be inspected. Therefore, the obtainingunit 41 may finely control the inclination of the λ/4 polarizing plate113.

The measurement light which has been subjected to the polarizationcontrol so as to be changed to the circular polarized light is focusedon a retina layer of the fundus Er through an anterior eye portion Ea ofthe eye to be inspected by a focus lens 114 mounted on a stage 116. Themeasurement light emitted to the fundus Er is reflected and scattered invarious retina layers and returns to the fiber coupler 104 through theoptical path described above.

On the other hand, the reference light divided by the fiber coupler 104is transmitted through a PM fiber 117 and emitted from a collimator 118as parallel light. As with the measurement light, the emitted referencelight is subjected to polarization control by a λ/4 polarizing plate 119which is disposed in a plane vertical to an optical axis of thereference light and which is inclined from P polarized light to Spolarized light by 22.5 degrees. The reference light is transmittedthrough a dispersion compensation glass 120, reflected by a mirror 122on a coherence gate stage 121, and returns to the fiber coupler 104.Since the reference light passes the λ/4 polarizing plate 119 twice,linearly polarized light is returns to the fiber coupler 104.

The coherence gate stage 121 is controlled by a driving controller so asto cope with uniqueness of an axial length of the eye to be inspected.

The measurement light and the reference light which have returned to thefiber coupler 104 are combined with each other so that interferencelight is obtained which is to be incident on the fiber coupler 123incorporating the polarizing beam splitter and which is divided intolight beams in different polarization directions (P polarized light andS polarized light in this embodiment) by a division rate of 50:50.

The P polarized light is transmitted through a PM fiber 124 and acollimator 130, divided by a grating 131, and received by a lens 132 anda line camera 133. Similarly, the S polarized light is transmittedthrough a PM fiber 125 and a collimator 126, divided by a grating 127,and received by a lens 128 and a line camera 129. Note that the gratings127 and 131 and the line cameras 129 and 133 are disposed so as tocorrespond to the individual polarization directions.

The light beams received by the line cameras 129 and 133 are output aselectric signals corresponding to light intensities, and the outputelectric signals are obtained by the obtaining unit 41.

Although the λ/4 polarizing plate 113 controls inclination using thepolarizing beam splitter as a reference, the inclination may becontrolled relative to a straight line which connects a center of anoptic disk to a center of a macula in a fundus. The same effect may beattained in a case where the polarizing beam splitter and the λ/4polarizing plates 113 and 119 are controlled using a vertical directionas a polarization reference.

Computer 200

The computer 200 of this embodiment is substantially the same as thecomputer 40, and therefore, a detailed description thereof is omitted.

Image Processing

Next, a signal processing method in polarization OCT will be described.In terms of segmentation of a retina layer, B scan is performed onlyonce on the same portion, and therefore, repetitive scan is notparticularly described hereinafter. However, to obtain 3D blood vesselinformation, a motion contrast feature value is required to be obtained,and therefore, B scan is required to be performed a plurality of timesalso in the second embodiment.

Generation of Tomographic Image and Generation of Fundus Image

The obtaining unit 41 performs reconstruction processing employed ingeneral spectral domain OCTs (SD-OCTs) on the interference signalsoutput from the line cameras 129 and 133. Then the obtaining unit 41generates two tomographic images based on polarization components (thatis, a tomographic image based on first polarized light and a tomographicimage based on second polarized light).

First, the obtaining unit 41 performs fixed pattern noise reduction onan interference signal. In the fixed pattern noise reduction, patternnoise is extracted by averaging a plurality of detected A scan signalsand subtracting the fixed pattern noise from the input interferencesignal.

Subsequently, the obtaining unit 41 converts a wavelength of theinterference signal into a wavenumber and performs Fourier transform soas to generate a tomographic signal (or a tomographic signal indicatinga polarization state).

By performing the process described above on the interference signals ofthe two polarization components, two tomographic images are generated.

Generation of Luminance Image

The obtaining unit 41 generates tomographic images indicatingintensities (hereinafter referred to as “luminance images” whereappropriate in this embodiment) using the two tomographic signalsdescribed above.

The luminance image is basically the same as a tomographic image ofgeneral OCTs, and a pixel value r is calculated in accordance withExpression 4 using tomographic signals A_(H) and A_(V) obtained by theline cameras 129 and 133.

r=√{square root over (A_(H) ² +A _(V) ²)}  Expression 4

In this embodiment, as with the first embodiment, the generation unit 44obtains 3D blood vessel information based on a tomographic imageindicating an intensity obtained in accordance with Expression 4.

Generation of DOPU image

The obtaining unit 41 calculates a Stokes's vector S for each pixel inaccordance with Expression 5 using the obtained tomographic signalsA_(H) and A_(V) and a phase difference Δφ between the tomographicsignals A_(H) and A_(V).

$\begin{matrix}{S = {\begin{pmatrix}I \\Q \\U \\V\end{pmatrix} = \begin{pmatrix}{A_{H}^{2} + A_{V}^{2}} \\{A_{H}^{2} - A_{V}^{2}} \\{2A_{H}A_{V}\cos \; {\Delta\varphi}} \\{2A_{H}A_{V}\sin \; {\Delta\varphi}}\end{pmatrix}}} & {{Expression}\mspace{14mu} 5}\end{matrix}$

Note that Δφ is calculated as “Δφ=φ_(V)−φ_(H)” using the phases φ_(H)and φ_(V) of the signals obtained when the two tomographic images arecalculated.

Subsequently, the obtaining unit 41 sets a window having a length ofapproximately 70 μm in a main scanning direction of the measurementlight and a depth of approximately 18 μm in a depth direction on B scanimages. Then the obtaining unit 41 averages elements of the Stokes'svector calculated for each pixel in accordance with Expression 5 in theindividual windows and degrees of polarization uniformity (polarizationuniformity DOPU) in the windows are calculated in accordance withExpression 6.

DOPU=√{square root over (Q_(m) ² +U _(m) ² +V _(m) ²)}  Expression 6

Note that Q_(m), U_(m), and V_(m) are values obtained by averagingelements Q, U, and V of Stokes's vectors in the windows, respectively.When this process is performed on all the windows of the B scan image, aDOPU image (or a tomographic image indicating polarization uniformity)is generated.

The DOPU is a numerical value indicating the polarization uniformity,and the numerical value is nearly 1 in a portion in which polarizationis maintained and is smaller than 1 in a portion in which polarizationis cancelled, that is, not maintained. A structure of a retina has acharacteristic in which a retinal pigment epithelium layer cancels apolarization state, and therefore, a portion corresponding to theretinal pigment epithelium layer in the DOPU image has the numericalvalue smaller than those of other regions. The DOPU image is obtained byimaging a layer which cancels polarization, such as the retinal pigmentepithelium layer, and accordingly, even in a case where the retinalpigment epithelium layer is deformed due to disease or the like, the RPEmay be more reliably imaged when compared with a change of luminance.

The generation unit 44 obtains segmentation information of the RPE fromthe DOPU image obtained by the obtaining unit 41. Specifically, a valueof the DOPU of the portion corresponding to the retinal pigmentepithelium layer is smaller than those of the other regions as describedabove, and therefore, the generation unit 44 extracts a region havingthe small DOPU value as the retinal pigment epithelium layer. Then thegeneration unit 44 may extract a lower end of the extracted retinalpigment epithelium layer as a layer boundary between the retinal pigmentepithelium layer and the Bruch membrane.

A method for determining a new blood vessel employed in the displaycontroller 46 is the same as that of the first embodiment, andtherefore, a description of a process performed by the displaycontroller 46 is omitted.

According to this embodiment, the layer boundary between the retinalpigment epithelium layer and the Bruch membrane may be easily detectedby PSOCT, and therefore, a blood vessel which intersects with the layerboundary between the retinal pigment epithelium layer and the Bruchmembrane and a blood vessel in the vicinity of the layer boundary may beeasily determined. In particular, a new blood vessel is likely tointersect with the layer boundary between the retinal pigment epitheliumlayer and the Bruch membrane, and therefore, the PSOCT is effectivelyused to specify a blood vessel which is a possible new blood vessel.

Other Embodiments

Embodiment(s) of the present invention can also be realized by acomputer of a system or apparatus that reads out and executes computerexecutable instructions (e.g., one or more programs) recorded on astorage medium (which may also be referred to more fully as a‘non-transitory computer-readable storage medium’) to perform thefunctions of one or more of the above-described embodiment(s) and/orthat includes one or more circuits (e.g., application specificintegrated circuit (ASIC)) for performing the functions of one or moreof the above-described embodiment(s), and by a method performed by thecomputer of the system or apparatus by, for example, reading out andexecuting the computer executable instructions from the storage mediumto perform the functions of one or more of the above-describedembodiment(s) and/or controlling the one or more circuits to perform thefunctions of one or more of the above-described embodiment(s). Thecomputer may comprise one or more processors (e.g., central processingunit (CPU), micro processing unit (MPU)) and may include a network ofseparate computers or separate processors to read out and execute thecomputer executable instructions. The computer executable instructionsmay be provided to the computer, for example, from a network or thestorage medium. The storage medium may include, for example, one or moreof a hard disk, a random-access memory (RAM), a read only memory (ROM),a storage of distributed computing systems, an optical disk (such as acompact disc (CD), digital versatile disc (DVD), or Blu-ray Disc (BD)™),a flash memory device, a memory card, and the like.

While the present invention has been described with reference toexemplary embodiments, it is to be understood that the invention is notlimited to the disclosed exemplary embodiments. The scope of thefollowing claims is to be accorded the broadest interpretation so as toencompass all such modifications and equivalent structures andfunctions.

This application claims the benefit of Japanese Patent Application No.2015-168287, filed Aug. 27, 2015, which is hereby incorporated byreference herein in its entirety.

What is claimed is:
 1. An ophthalmic apparatus comprising: a generationunit configured to generate 3D blood vessel data indicating a bloodvessel in a fundus based on a plurality of tomographic image dataindicating cross sections of the fundus; a boundary obtaining unitconfigured to obtain layer boundary data indicating at least one layerboundary based on 3D tomographic image data including the plurality oftomographic image data indicating the cross sections of the fundus; anda determination unit configured to determine a blood vessel intersectingwith the layer boundary by comparing the 3D blood vessel data with thelayer boundary data.
 2. The ophthalmic apparatus according to claim 1,further comprising a display controller configured to cause a displayunit to display at least one of a 3D blood vessel image indicated by the3D blood vessel data and a 2D blood vessel image obtained by integratingthe 3D blood vessel data in a depth direction of the fundus, and tocause the display unit to display a blood vessel determined by thedetermination unit in a state in which the blood vessel determined bythe determination unit is distinguished from other blood vessels.
 3. Theophthalmic apparatus according to claim 1, wherein the boundaryobtaining unit obtains layer boundary data indicating at least one layerboundary based on the 3D tomographic image data including a plurality oftomographic image data indicating cross sections of the fundus to beused in generation of the 3D blood vessel data.
 4. The ophthalmicapparatus according to claim 2, wherein the display controller causesthe display unit to display layer boundaries indicated by the layerboundary data which are superposed on the 3D blood vessel image.
 5. Theophthalmic apparatus according to claim 1, wherein a plurality oftomographic image data indicating cross sections of the fundus to beused in generation of the 3D blood vessel data is different from aplurality of tomographic image data indicating cross sections of thefundus included in the 3D tomographic image data, and angles of field ofthe plurality of tomographic image data indicating the cross sections ofthe fundus to be used in generation of the 3D blood vessel data aresmaller than angles of field of the plurality of tomographic image dataindicating the cross sections of the fundus included in the 3Dtomographic image data.
 6. The ophthalmic apparatus according to claim1, wherein the layer boundary data indicates a plurality of layerboundaries, and the determination unit determines a blood vesselintersecting with a layer boundary selected from among the plurality oflayer boundaries.
 7. The ophthalmic apparatus according to claim 6,wherein the display controller displays a 2D tomographic image based onthe 3D tomographic image data in the display unit and the plurality oflayer boundaries superposed on the 2D tomographic image, and thedetermination unit determines, in a case where the layer boundarydisplayed in a state in which the layer boundary is superposed on the 2Dtomographic image is selected, a blood vessel intersecting with thelayer boundary selected from among the plurality of layer boundaries. 8.The ophthalmic apparatus according to claim 1, wherein the layerboundary data indicates at least one of a boundary between a Bruchmembrane and a retinal pigment epithelium layer and a boundary betweenthe Bruch membrane and a choroid layer.
 9. The ophthalmic apparatusaccording to claim 1, further comprising a display controller configuredto cause a display unit to display a blood vessel image based on the 3Dblood vessel data and cause the display unit to display the blood vesseldetermined by the determination unit in a color different from a colorof other blood vessels.
 10. The ophthalmic apparatus according to claim1, wherein a blood vessel image based on the 3D blood vessel data isdisplayed in a display unit and an object indicating a blood vesseldetermined by the determination unit is displayed in the display unit.11. The ophthalmic apparatus according to claim 9, wherein the 3Dtomographic image data is obtained by polarization sensitive opticalcoherence tomography.
 12. An information processing method comprising:generating 3D blood vessel data indicating a blood vessel in a fundusbased on a plurality of tomographic image data indicating cross sectionsof the fundus; obtaining layer boundary data indicating at least onelayer boundary based on 3D tomographic image data including theplurality of tomographic image data indicating the cross sections of thefundus; and determining a blood vessel intersecting with the layerboundary by comparing the 3D blood vessel data with the layer boundarydata.
 13. A non-transitory storage medium storing a program which causesa computer to execute the information processing method set forth inclaim
 12. 14. An ophthalmic apparatus comprising: a generation unitconfigured to generate blood vessel data indicating a blood vessel in afundus based on a plurality of tomographic image data indicating crosssections of the fundus; a boundary obtaining unit configured to obtainlayer boundary data indicating at least one layer boundary based on thetomographic image data indicating the cross sections of the fundus; anda determination unit configured to determine a blood vessel intersectingwith the layer boundary by comparing the blood vessel data with thelayer boundary data.
 15. An ophthalmic apparatus comprising: ageneration unit configured to generate 3D blood vessel data indicating ablood vessel in a fundus based on a plurality of tomographic image dataindicating cross sections of the fundus; a boundary obtaining unitconfigured to obtain layer boundary data indicating at least one layerboundary based on 3D tomographic image data including the plurality oftomographic image data indicating the cross sections of the fundus; anda display controller configured to cause a display unit to display layerboundaries indicated by the layer boundary data which are superposed ona 3D blood vessel image indicated by the 3D blood vessel data.